Neutron Sources & Energies
Neutrons are classified according to their energy. The following is a listing of the terms used to describe the various classifications, followed by the basis for each term, and then the range of neutron energies that defines the class:
Thermal
- Neutrons in thermal equilibrium with their surroundings
- Most probable energy at 20 degrees (C) – 0.025 eV; Maxwellian distribution of 20 degrees (C) extends to about 0.2 eV.
Epithermal
- Neutrons of energy greater than thermal
- Greater than 0.2 eV
Cadmium
- Neutrons which are strongly absorbed by cadmium
- Less than 0.4 eV
Epicadmium
- Neutrons which are not strongly absorbed by cadmium
- Greater than 0.6 eV
Slow
- Neutrons of energy slightly greater than thermal
- Less than 1 to 10 eV (sometimes up to 1 keV)
Resonance
- In pile neutron physics, usually refers to neutrons which are strongly captured in the resonance of U-238, and of a few commonly-used detectors (e.g., Indium, Gold, etc.)
- 1 eV to 300 eV
Intermediate
- Neutrons that are between slow and fast
- Few hundred eV to 0.5 MeV
Fast
Utrafast
- Relativistic
- Greater than 20 MeV
Pile
- Neutrons of all energies present in nuclear reactors
- 0.001 eV to 15 MeV
Fission
- Neutrons formed during fission
- 100 keV to 15 MeV (Most probable – 0.8 Mev; Average – 2.0 MeV)